The present invention provides a method of curing a coating of plastisol or organosol on a massive object. More particularly, the method involves keeping latent solvent in the vicinity of the coating at elevated temperatures.
Polyvinylchloride (PVC) is generally made into coatings by means of plastisol or organosol technology. Plastisol technology involves the use of plasticizers. Polyvinyl fluoride (PVF) coatings are generally made by using organosol technology.
PVF organosols are made by suspending fine powder PVF in latent solvent which does not dissolve the PVF at room temperature (26.degree. C.) but does go through two phases as temperature is increased. First a gel is formed at intermediate temperatures, and then, with increased heating, a true solution is formed. Coating coalescence starts at the gel temperature and proceeds more rapidly with increasing temperature. Of course, when a solution is formed and the solvent later evaporates, coalescence is complete. One difficulty is that certain latent solvents for PVF are quite volatile or even boil at atmospheric pressure at temperatures near or even below the gel and solution temperatures. This can make it particularly difficult to coalesce coatings onto massive objects, particularly if they are heated from the outside. The problem is that the latent solvents evaporate from the outer layers of the coating composition before the inner layers are at high enough temperatures for long enough to gel and coalesce.
Polyvinyl fluoride (PVF) is generally not soluble at room temperature in conventional solvents, however, it can be put into solution with so called latent solvents. A dispersion of PVF powder is suspended in latent solvent and heated to a first temperature at which a gel is formed and then to a higher second temperature at which a solution is formed. The heating can be done continuously without stopping at the first temperature. Latent solvents and other technology useful in handling PVF are discussed in U.S. Pat. No. 2,953,818--Barton (Sept. 27, 1980) and U.S. Pat. No. 3,139,470--Prengle et al. (June 30, 1964), both incorporated herein by reference.